PMC

Dunes emerging on an initially flat sand bed under bimodal wind regime. In all images, arrows indicate the wind directions. (A) Snapshot of simulation with u _* = 0.4 m/s, T _w ≈ 12 days and θ_w = 40° at time T = 150T _w. (B) Seif dunes obtained from the simulation with same parameters as in A but with θ_w = 120°, at T = 300T _w. (C) seif dunes of height ≈20 m obtained using different values of T _w with θ_w = 120° and T = 300T _w. Results are expressed in terms of t _w = T _w/T _m where T _m ≈ 10⁸s is the migration (or reconstitution) time of a transverse dune with the height of the seif dunes shown in the images; dune fields in A–C have length of 1 km. (D) Top view of a seif dune with height of ≈25 m within a dune field obtained with θ_w = 120° and t _w ≈ 10⁻². Small transverse dunes, with height of a few meters, inciding obliquely onto the seif dune in the center can be seen. The image has dimensions 1700 m × 400 m. (E and F) Crest position y _crest (E) and crest height h _crest (F) of the seif dune shown in (d) as function of the position in the resultant wind direction, x (to the right in the image).

The results of trajectory and landmarks estimated by SEIF (a) and iterative SEIF (ISEIF) (b).

Seif, the driver, is elected as staff of the month and receives a T-shirt. KENYA

The RMS errors of positions and headings of SEIF (a) and ISEIF (b).